Which of the following is NOT part of the upper extremities?

The patella is a sesamoid bone located in the knee, serving as a protective structure for the knee joint and aiding in its function. It is specifically associated with the lower extremities, as it is part of the leg. In contrast, the humerus is the upper arm bone, the scapula is the shoulder blade, and the metacarpals are the bones in the hand that connect the wrist to the fingers. All these other options belong to the upper extremities, which consist of the arm, shoulder, and hand. Therefore, identifying the patella as the structure not associated with the upper extremities is accurate.